Range and geography shaped the submarine force

Short patrols supported by Malta, Gibraltar, and Alexandria differed sharply from the far longer routes expected from Singapore toward Japanese waters. A Mediterranean boat could trade range for agility, while a Far East force needed the endurance to cross the South China Sea and reach the approaches to Japan. Transit distance affected fuel use and the number of submarines needed to keep boats on station while others returned for maintenance. British plans envisioned using long-range submarines offensively to interdict Japanese traffic between Japan, Korea, and the China coast. Each design therefore reflected its bases, geography, and intended campaign.